As electric linear motion actuators of this type including an electric motor as a driving source, electric linear motion actuators as discussed below are known.
In the electric linear motion actuators disclosed in Japanese Unexamined Patent Application Publication No. 2010-65777and Japanese Unexamined Patent Application Publication No. 2013-96522, planetary rollers are incorporated between a rotary shaft configured to be rotated by an electric motor and an axially movably supported outer ring member, when the rotary shaft rotates, the respective planetary rollers rotate about their axes while revolving around the rotary shaft due to the frictional contact of the planetary rollers with the rotary shaft, and a helical rib formed on the inner diameter surface of the outer ring member engages in a helical groove or circumferential grooves formed in the outer diameter surface of each planetary roller, thereby moving the outer ring member in the axial direction.
In the electric linear motion actuators disclosed in Japanese Unexamined Patent Application Publication Nos. 2010-65777and 2013-96522 the outer ring member is a cylindrical member having both open ends. In this arrangement, if foreign objects go into the outer ring member from the end opening of the outer ring member on the outboard side of the outer ring member, the biting/entry of the foreign objects into the outer ring member may hinder the rotation of the planetary rollers, so that the outer ring member may not be able to move in the axial direction.
In order to overcome such a problem, in the electric linear motion actuators disclosed in Japanese Unexamined Patent Application Publication Nos. 2010-65777and 2013-96522, a cap member is press-fitted to the interior of an open end of the outer ring member so as to close the opening of the outer ring member. However, since the cap member made of metal is press-fitted to the outer ring member made of metal, there is a problem regarding the seal performance.
It is possible to overcome such a problem by providing a member made of rubber or resin between the press-fitting surfaces of the cap member and the outer ring member, or by using the cap member made of rubber or resin. However, in case that the driven member configured to be linearly moved by the outer ring member is a brake pad of the electric brake system, the rear surface of the brake pad reaches a high temperature, specifically, 200 to 300 degrees Celsius. As a result thereof, the deterioration of resin or rubber tends to occur so that a problem may occur regarding the durability.
It is an object of the present invention to improve seal performance in an electric linear motion actuator configured to linearly drive a linear motion member due to the rotation of a rotary shaft.